Seat belt apparatuses that take up a webbing to restrain a vehicle occupant in an emergency of a vehicle include a seat belt apparatus in which an airbag is provided along a webbing, and the airbag is inflated with gas in an emergency of a vehicle. This seat belt apparatus is sometimes referred to as an airbelt apparatus.
Japanese Unexamined Patent Application Publication No. 2001-260807 describes providing a webbing guide along this airbag and slidably passing a webbing through this webbing guide. Japanese Unexamined Patent Application Publication No. 2001-260807 describes that this airbag is folded, and is surrounded by an exterior cover made of fabric. During the inflation of the airbag, the sewing thread breaks, and this exterior cover opens.